DNS filter causing certificate errors.

[6sITdept]

We renewed our firewall services.  The previous agreement expired last Friday (12/7/2018).  therefore our new agreement was activated that day.  Nothing happened over the weekend.  

However on Monday, no one locally could access the Internet.  personally when I used Chrome, it gave us this message: err_cert_common_name_invalid.  Other messages like, "Names dont match" appeared.

When we restarted the firewall, there would be a brief moment of connection, before getting this error again.  A few other sites would say "you've been blocked" (google was one of them).  

After I turned off the DNS Filter, we were all able to access the internet again.   Would the switch over from the old agreement to the new agreement cause this issue?  Any ideas what to do?  THis is not ideal how we want the firewall to go.

We are using a Fortigate 100E. our firmware is 5.4.6